Chitin is a polymer of beta-1,4-(2-deoxy-2-acetamidoglucose) which occurs widely in nature and is a principal constituent of the exoskeleton of many arthropods and insects, and of the cell wall of many fungi. It is frequently found in a mixture with proteins and calcium compounds. It consists essentially of a polymer of 2-deoxy-2-acetamidoglucose monomer units that are linked in beta-1,4 fashion though a minor fraction of said units may be hydrolyzed to 2-deoxy-2-aminoglucose units.
The term chitosan is generally applied to copolymers having greater than 65% 2-deoxy-2-aminoglucose monomeric units and the remainder monomeric units being 2-deoxy-2-acetamidoglucose units. Chitosan is derived from chitin by hydrolysis of some 2-deoxy-2-acetamidoglucose units to 2-deoxy-2-aminoglucose units. Due to the presence of free amino groups, chitosan is soluble in aqueous acidic solutions and is present in such media as a polycation with the protonated amino group bearing a positive charge. Polycations are known to aid flocculation.
The reaction of polymeric amines such as chitosan with halogenating agents has been studied only sparsely. Y. Shigeno, K. Kondo, and K. Takemoto [Journal of Applied Polymer Science, Vol. 25, 731-738 (1980)] studied the reaction of chitosan with solutions of iodine in various solvents including water. They found that the only products formed were deeply colored charge transfer complexes that were produced over a period of days at 30.degree. C. No evidence of iodination of the amino group was found.
T. Uragami, F. Yoshida, and M. Sugihara [Makromol. Chem., Rapid Commun., Vol. 4, 99 (1983)] found that chitosan-containing membranes actively transport chloride ions. Chloride ions bear a negative charge and are therefore not capable of acting as halogenating agents by donating positively charged chlorine. As would be anticipated, no N-chlorinated species were observed in this study.
K. Takeda, K. Shimazu, and M. Goto (Japan Kokai Tokkyo Koho JP 01 11,101, Jan. 13, 1989) treated chitosan in solution with chlorine dioxide. The molecular weight of the chitosan polymer was thereby reduced from 360,000 to 60,000, but there was no incorporation of chlorine into the chitosan, and hence no 2-deoxy-2-chloraminoglucose monomeric units in the product.
H. Sano, H. Itoi, and N. Kobiyama (Jpn. Kokai Tokkyo Koho JP 60,186,504, Sep. 24, 1987) reacted an aqueous dispersion of high molecular weight chitosan with chlorine gas at 10.degree.-70.degree. C. The product isolated was chitosan with a reduced molecular weight of 20,000. No incorporation of chlorine into the product was reported.